The present invention relates to a process and an apparatus for coupled liquid chromotography and nuclear magnetic resonance (NMR) spectroscopy measurements whereby components of a sample were detected and separated using liquid chromotography and whereby these components were measured afterwards using nuclear resonance spectroscopy.
Such a process and such an apparatus are known, for example from J. Chromatography 186, 497, (1979), "On-line Coupling of High-Performance Liquid Chromatography and Magnetic Resonance".
In a pure on-line coupling, the NMR-spectrometer is directly coupled after the liquid chromatograph.
During the HPLC-measurement (HPLC equals High Performance Liquid Chromatography) of a continuous-flow process, the eluent and the resulting peaks are fed continuously and sequentially into the NMR-spectrometer to be spectrometrically examined "on-line" therein.
As an alternative to the continuous-flow-process the stop-flow technique is used, whereby the flow pump delivers the eluent only during certain time periods. The flow pump stops as long as a component is inside the NMR-spectrometer.
The obtained NMR signal sensitivity in dependence on the concentration of the pertinent component can be insufficient with the continuous-flow process, since the retention time in the NMR measuring head is limited.
The obtained chromatographical separation efficiency for the subsequent components, which are still in the separation column, is deteriorated in the stop-flow process because of diffusion.